Yes it's just the adults that you really have to worry about escaping. If you have a good lid for the 20 gallon then you should be good to go. Although I'd only keep then in the air tight containers (with air holes of course). I have found P. Nivea in areas with lots of large oak trees. They come to my lights often. If you are willing to spend some money for a light you can pick up a bug zapper at Lowes. It was the 40 watt unit and I sawed off the plastic housing, cut the - and + wires going to the metal grid and wrapped them separately in electrical tape, and removed the metal grid. It attracts so many species of insects every night.